Is the roller coaster G force threat all spin?

Penn scientists find that coaster G's, twists, and speeds are not enough to injure the brain

(Philadelphia, PA) -- To meet the growing expectations of thrill-seekers, amusement park rides have been built bigger, faster, and more exciting. But do bigger thrills come with added risks of injury? Published medical case studies have proposed a link between roller coaster forces and brain injury. Already the State of New Jersey has enacted legislation limiting G forces, and similar legislation has been proposed by members of the U.S. House of Representatives.

According to a pair of researchers at the University of Pennsylvania, however, medical science does not support the notion that roller coasters produce forces large enough to harm the brains of riders. Their findings are presented in the October issue of the Journal of Neurotrauma.

"We should step back and separate the facts from the hype," said Douglas H. Smith, MD, from the Department of Neurosurgery and the Head Injury Center at the Penn School of Medicine and co-author of the study. "To our knowledge, no peer-reviewed studies have definitively linked brain injury in healthy individuals to riding the latest, and most powerful roller coasters. In fact, G forces really aren't the issue here."

Most people are familiar with the dangers of G forces as they affect pilots, as popularized in film and television. Just as unsuspecting car passengers are forced against the door during sharp turns, pilots feel accelerations as they make quick maneuvers -- except for pilots, these accelerations can be as much a five to nine times the force of gravity (or Gs). The biggest risk of high Gs is a loss of consciousness as blood pools in the limbs and away from the brain. But these effects are from sustained Gs over an average of 43 seconds. High G maneuvers on roller coasters, however, rarely last more than three seconds. As the researchers point out, an average person could momentarily experience eight to ten Gs by plopping down onto the couch to watch Top Gun.

"What we should be concerned about is not G forces, but the effects of rapid head acceleration -- the rotational force on the brain that occurs as the body quickly changes directions," said co-author David F. Meaney, PhD, of Penn's Department of Bioengineering, "And, when we predict head accelerations in roller coasters -- the sudden twists and turns -- we find that they are well within established safety margins. It does not appear that roller coasters produce high enough forces to mechanically deform and injure the brain."

Using a simple mathematical model, the researchers examined the three basic features of G forces as experienced by riders: the magnitude of the force, the direction of the acceleration, and the time interval over which the acceleration occurs. They acquired G force data from three of the most popular and powerful roller coasters in the country: the "Rock 'n' Roller Coaster" at the Disney-MGM Studios in Orlando, Florida; "Speed -- The Ride" at the Nascar Café, in Las Vegas, Nevada; and "Face-Off" at Kings Island, Ohio. Using this data, they calculated peak head accelerations in three directions, assuming the head did not strike a surface. Even considering the worst-case scenario, the researchers found that the largest forces experienced on roller coasters were far below those that are known to cause injury. In fact, the damage reported in some published case reports trauma done as a result of pre-existing brain injuries. Even in those cases, researchers said that other factors, such as hypertension from the excitement of the being on the ride, should be considered.

"The amount of rotational acceleration known to create injury in the white matter of the brain are roughly 18 times higher than the maximum accelerations calculated on the roller coasters," said Smith. "For healthy people who meet the size requirements for the ride, you are probably safer on the average roller coasters than driving to the amusement park."